Methods and apparatus for efficient wakeup of wireless device

ABSTRACT

In a described example, an integrated circuit includes an input coupled to receive a plurality of beacon frames, the beacon frames include an indication of data transmissions available for a device that includes the integrated circuit. The integrated circuit also includes a controller configured to compare the plurality of beacon frames to determine a plurality of bytes prior to the indication of data transmission available that is present in each of the plurality of beacon frames and is configured to provide a signal indicating a low power mode in which the device does not receive transmissions and to provide a signal indicating a wake mode at a selected time before transmission of the plurality of bytes in a subsequent beacon transmission.

TECHNICAL FIELD

This relates generally to wireless communications, and, in particular,to conserving power in wireless transceiver devices.

BACKGROUND

Wireless devices are becoming ubiquitous. These devices use a number ofwireless transmission standards. The most common are the IEEE 802.11standards, commonly known as Wi-Fi or wireless LAN (WLAN). Wi-Fi iscommonly used to connect devices to the Internet. One area of rapiddevelopment with regard to wireless Internet connections is the“Internet of Things” (IoT). “Normal” connections to the Internet involvesome type of computer, such as a laptop or smart phone. IoT devices usewireless or wired connections to the Internet for various purposes. AnIoT appliance may include a Wi-Fi module to allow the manufacturer tomonitor operation of the appliance, suggest when maintenance isnecessary, update control firmware, automatically order supplies, ordiagnose problems.

In an IoT device such as an appliance, power consumption by the IoTdevice is not a large concern because the appliance draws power from thehome's power system. However, not all IoT devices have access to a wiredsupply or can be conveniently wired into a power source. For example,motion sensors can be used for security systems and for automaticlighting. An outlet is rarely available at the optimal position forthese devices and it is very expensive to provide custom wiring to thedevice. Therefore, it is desirable to operate these devices usingbattery power. In addition, it is desirable to have long battery life tominimize the need to replace the batteries in these devices. However,the wireless function must be connected to the network (local orInternet) in order to fully function. Therefore, for these batterypowered devices, it is important that the wireless connection consume aslittle power as possible.

SUMMARY

In accordance with an example aspect, an integrated circuit includes aninput coupled to receive a plurality of beacon frames, the beacon framesinclude an indication of data transmissions available for a device thatincludes the integrated circuit. The integrated circuit also includes acontroller configured to compare the plurality of beacon frames todetermine a plurality of bytes prior to the indication of datatransmission available that is present in each of the plurality ofbeacon frames. The integrated circuit is configured to provide a signalindicating a low power mode in which the device does not receivetransmissions and to provide a signal indicating a wake mode at aselected time before transmission of the plurality of bytes in asubsequent beacon transmission.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a basic Wi-Fi configuration.

FIG. 2 is a diagram of a beacon frame.

FIG. 3 is a beacon frame diagram illustrating the BET technique.

FIG. 4 is a histogram of a feature of sample beacon frames.

FIG. 5 is a histogram of another feature of sample beacon frames.

FIG. 6 is a flow diagram of an aspect method.

FIG. 7 is a schematic diagram of an aspect station.

FIG. 8 is an experimental trace graph.

FIG. 9 is another experimental trace graph.

FIG. 10 is a schematic diagram of another aspect station.

DETAILED DESCRIPTION

Corresponding numerals and symbols in the different figures generallyrefer to corresponding parts unless otherwise indicated. The figures arenot necessarily drawn to scale.

The term “coupled” may include connections made with interveningelements, and additional elements and various connections may existbetween any elements that are “coupled.”

This description provides examples using the IEEE 802.11 (Wi-Fi or WLAN)standards. However, the teachings of this specification are applicableto various wireless digital transmission formats. The Institute forElectrical and Electronic Engineering has promulgated the basicstandards for Wi-Fi under IEEE Standard 802.11-2012 (“Wi-Fi Standard”),which is hereby incorporated in its entirety herein. Additionalstandards, such as IEEE 802.11ac, are additions to this basic standard.

FIG. 1 is a diagram of a basic Wi-Fi configuration 100. Access point(AP) 102 broadcasts in area 106. The stations shown in FIG. 1 aresmartphone 104-1, tablet 104-2 and laptop 104-3. The AP and the stationsinclude a transceiver. The structure of the signals communicated betweenthe stations and the access point is determined by the configuration ofthe access point. One of the key ways configuration information andother link information can be transmitted from the access point to thestations is a beacon signal. The beacon signal is a specific type ofmanagement frame that is transmitted on a periodic basis. Other digitalwireless transmission standards use other signals, but nearly allstandards have management signals similar to the beacon frames used inWi-Fi. For network synchronization purposes. One important field in thebeacon signal is the Traffic Indication Map (TIM). The TIM includes anindication of available data transmissions for all stations in thecoverage area of the access point. In a beacon signal for a particularstation, the TIM includes data indicating if the access point hasreceived data from the terrestrial network (i.e. the Internet) for thatstation.

The need to continually receive the beacon signal is not a problem forstations that have ample power resources. However, if power resourcesare an issue, continuous reception can place a severe strain on astation's power resources. One technique for lowering power consumptionis a sleep mode. This technique is a part of the Wi-Fi specification. InWi-Fi networks the sleep mode takes advantage of the regular nature ofbeacon transmission. In most AP installations, the beacon is transmittedat a regular interval (e.g. every 102.4 milli-seconds.) However, thespecifics of beacon transmission are provided to the station upon linkinitiation, so that the station knows precisely when the beacon framewill be transmitted. With a sleep mode, the receiving/decoding circuitryin the station is disabled until just before the beacon frame istransmitted. During link setup, the station can tell the AP that it isusing sleep mode. The AP then buffers data traffic designated for thesleeping station until the station is scheduled to wake up and receive abeacon frame. Fields in the beacon frame tell the station that there iswaiting buffered data.

The use of sleep modes significantly reduces the power consumed by thestation. However, receiving and decoding the beacon frame can alsoconsume a significant amount of power. FIG. 2 is a diagram of a beaconframe 200. Beacon frame 200 begins with a physical layer convergenceprotocol (PLCP) segment 202. This segment is a standard configuration of192 bits and is designed to enable stations to obtain synchronizationwith the beacon frame. The beacon frame is composed of many segments,but for simplicity only two are shown. The traffic indication map (TIM)204 informs the station if there is buffered data to be pulled. Thebeacon frame ends with a frame check sequence (FCS) 206 that includes a32-bit cyclic redundancy check (CRC). The CRC allows for error detectionand correction. As noted in FIG. 2, the beacon frame occupiesapproximately 2 mSec. With standard sleep mode, the station must wake upbefore the beacon frame arrives and then decode the entire beacon frame.Receiving and decoding the entire beacon frame is a significant use ofpower resources for the station. If there is no data stored for thestation, the power used to receive the beacon signal does not result inany data transfer.

One technique for reducing the power consumed by beacon frame receptionis beacon early termination (BET). FIG. 3 is a beacon frame diagramillustrating the BET technique. When a station is in sleep mode, it mustwake up to receive its scheduled beacon transmission. The TIM frameindicates if there is data queued for stations in the area served by theAP. Therefore, the TIM is the one data segment that the station mustreceive to determine if there is data buffered for the station. In BET,the station wakes up from low power (sleep) mode in time to receive thebeacon frame, but stops receiving and returns to sleep mode afterreceiving the TIM, if there is no data waiting for it. The TIM isusually one of the earlier segments in the beacon frame. Thus, the BETtechnique conserves significant power resources.

FIG. 4 is a histogram of the position of the TIM in a sample of beaconframes. As shown in histogram 400 of FIG. 4, the TIM is usually at the58^(th) or 62^(nd) byte of the beacon frame. Histogram 400 wasdetermined experimentally by analyzing beacon frames transmitted by 198APs. The beacon frame configuration is consistent on a single AP, so thehistogram shows numbers of APs having the TIM at the indicated location.As shown in frame 300 of FIG. 3, using BET, the wake time for thestation is usually reduced from 2 mSec in normal sleep mode toapproximately 700 μSec in BET mode. Because the FCS (206, FIG. 2) is notreceived, there is a marginal increase in the risk of data corruption,but this risk is not significant. Thus, the wake up time using BET isless than half of the normal sleep mode with a concomitant reduction inpower consumed. However, because the BET technique receives and decodesthe portion of the beacon frame that is received before the TIM, thereis still some power that is wasted in receiving and decoding unnecessaryinformation when the station needs to receive the TIM information.

In an aspect of the present application, the wake time is minimized bydetermining a constant block of bytes that is transmitted prior to theTIM within the beacon frame. FIG. 5 is a histogram of another aspect ofsample beacon frames. Histogram 500 uses data from the beacon frames of198 APs. Histogram 500 shows that the number of constant bytes (i.e.bytes that are the same in every beacon frame transmitted by that AP)ranges from 21 bytes to 210 bytes. Part of this group of constant bytesor “barker” is used by the receiving station as a substitute to thetraditional PLCP preamble to reduce the overall receiving time requiredfor TIM reception. This method shown in FIG. 6. In an aspect, the barkeris selected so that there is at least a predetermined amount of timebetween the barker and the TIM to allow for proper synchronization ofthe received data by the station.

FIG. 6 is a flow diagram of an aspect method 600, which is performed bya station. The method 600 may be implemented on an integrated circuit(s)and/or by using discrete components, or by using programmable componentssuch as processors or microcontrollers. In step 602, the stationinitiates contact with an access point. The station then receives atleast N beacon frames in step 604. For example, N could equal 20. Instep 606, the N beacon frames are compared to each other to find aseries of bytes in every beacon frame that is at least M bytes long andthat is prior to the TIM field. This series of bytes is the barker. Inan example, M is equal to at least twelve bytes. In step 608, it isdetermined if an appropriate barker is found. If not, the method goes tostep 610 and defaults back to standard sleep mode (or another powersaving process, like BET).

If a suitable barker is found at step 608, the method goes to step 612and enters low-power mode. Any sleep mode that lowers power consumptionduring the time the station is not listening for the barker and TIM maybe employed.

The station knows the schedule for beacon signal transmission from theinitial link setup with the AP. In addition, the station knows thetiming of the barker within the beacon frame from step 606. With thepredefined AP configuration and with the station enabling L2 power savemode (which is communicated to the AP), the AP will buffer all multicastand unicast frames until the next delivery TIM (DTIM) beacon, which maybe every one, two, or N beacons according to the AP configuration.Therefore, the station waits in sleep mode until a wakeup period of xμSec before the barker is expected, and then listens for the barker instep 614. For example, x may be 150 μSec. This wake up period isdependent on the sleep mode employed and the circuitry of the station.Any wakeup period that enables the station to be ready to receive thebarker may be suitably employed. The station uses the barker rather thanthe PLCP (202 FIG. 2) to synchronize with the portion of the beaconframe including the barker and the TIM. The incoming beacon frame iscompared to the selected barker using, for example, a comparator, untilthe barker is identified in the incoming beacon frame. The station thenreceives the TIM and determines if the TIM was correctly received instep 618. If so, the process continues to step 622 to determine if thereare buffered frames to be received. The frames are then pulled from theAP in step 624. Step 626 determines if there are more frames to receive.If so, the process loops back to step 624. If not, the method returns tostep 614 to wait and to wake for the next scheduled TIM beacon.

Of note, in certain sleep modes under the 802.11 standards, a particularstation is not required to listen for the TIM in each beacon frame, butrather in every second or third, etc. frame. That is, after receivinginformation that the station is using sleep mode, the AP will only sendTIM information for that station every second, third, etc. beacon frame.The wakeup performed in step 614 may then occur only when a beacon framethat is scheduled for this station is broadcast, thus saving additionalpower.

Returning to FIG. 6, if the TIM is not received or received incorrectlyat step 618, the station determines in step 620 if this is, for example,the third TIM reception failure. If not, the process returns to step612. If this is the third failure, it is assumed that the current barkeris not providing accurate TIM reception. From this point there are twooptions, which are design choices as indicated by the solid and dashedpath lines in FIG. 6 leaving state 620. In one choice, the stationreverts to standard sleep mode or BET mode as in step 610. In the otherchoice, the station may return to step 602 and try to determine a betterbarker signal. This design choice is indicated in FIG. 6 by the dashedline. In an additional aspect, an additional step (not shown) determinesif no barker is detected x μSec after wake up, for example, 500 μSec. Ifso, the process switches to use the BET mode or can use traditional fullreception of the beacon frame. Thus, if the barker is not detected afterx μSec, for example, because a false barker (i.e. incorrect barker thatthe AP does not use) has been selected, because the AP has delayed thebeacon frame transmission, the TIM will still be received.

FIG. 7 is a schematic diagram of an aspect station capable of executingmethod 600 of FIG. 6. The beacon frames are received and decoded byreceive and decode unit 704 via antenna 702 (see step 604, FIG. 6). Thebeacon frames in digital form are passed to controller 710. Controller710 analyzes the first N frames to determine a barker (steps 606 and608, in FIG. 6). The controller 710 then executes the sleep mode anddetermines the wake time based on the configuration data from the AP,the analysis of the N beacon frames and the position of the barker(steps 612 and 614, FIG. 6). After waking, controller 710 then comparesthe incoming beacon frame to the barker and determines when the barkeris detected (step 614, FIG. 6). Controller 710 then receives the portionof the beacon frame including the TIM and determines if the TIM wasproperly received and determines if there is data queued in the APwaiting to be pulled (steps 614, 618 and 620). In alternative aspect,all of the functions of FIG. 7 except for antenna 702 are include in anintegrated circuit. In yet another alternative aspect, an integratedcircuit includes RF circuitry for receiving the RF signal from antenna702; while the decode functions of receive and decode unit 704 andcontroller 710 are performed by a processing core on the integratedcircuit under the control of software to perform the steps of method 600(FIG. 6).

The power savings of the method of FIG. 6 is shown experimentally inFIGS. 8 & 9. FIG. 8 is an experimental trace graph 800 illustrating theBET technique where trace 802 shows the beacon frame and trace 804 showsthe consumption of current by the station. Period 806 is the wake upperiod required for the station. A corresponding increase in consumptionof current by the station is shown during this period in trace 804.During period 808, the station is receiving and decoding the beaconsignal. The station of FIG. 8 uses the BET method. In this example, theTIM ends approximately 712 μSec after the beginning of the beacon frame.Thus, the station ends reception at the end of period 808 and returns toa sleep mode.

In contrast to the trace of FIG. 8, FIG. 9 is another trace graph 900showing reception of the same beacon frame 902, but now using the methodof FIG. 6. The beginning of the barker is approximately 176 μSec beforethe end of the TIM. Therefore, after a wakeup period 906 of 150 μSec,full reception only occurs during period 908, which is less than aquarter of period 808 (FIG. 8). Thus, FIGS. 8 & 9 demonstrate that usingthe method of FIG. 6, the receiver is in wake mode much less than eventhe BET process, and thus the method of FIG. 6 is more power efficientthan the BET method.

FIG. 10 is a schematic diagram of another aspect station 1000. Station1000 includes two reception paths, wake reception and decode path 1004and barker detect and TIM decode path 1006. Controller 1010 controls theoperation of both paths and uses switch 1008 to select between thesepaths. Both paths receive signals from the AP via antenna 1002. Undernormal wake reception, controller 1010 selects wake reception and decodepath 1004. However, to execute steps 614 and 618 (FIG. 6) the barkerdetect and TIM decode path 1006 is used. Barker detect and TIM decodepath 1006 includes data reception circuitry and pattern matchingcircuitry to allow for quick and power efficient detection of thebarker. Once the barker is detected, barker detect and TIM decode path1006 includes circuitry designed for receiving and decoding the TIM.Because this circuitry is designed for one type of data segment, it isdesigned to perform this specific task using minimal power. Thecontroller 1010 uses the TIM data to determine if data for the stationis queued in the AP. If not, the controller continues to enable barkerdetect and TIM decode path 1006 during the wake period for TIMreception. Therefore, even during the wake up periods to receive the TIMwithin the beacon frame (such as periods 906 and 908 (FIG. 9)), station1000 operates with very high efficiency. If the TIM indicates that datais queued for station 1000, the controller 1010 enables wake receptionand decode path 1004 to allow for normal reception of the data to betransmitted to station 1000. In an alternative aspect, all of thefunctions of FIG. 10 except for antenna 1002 are include in anintegrated circuit. In yet another alternative aspect, an integratedcircuit includes separate RF circuitry for receiving the RF signal fromantenna 1002 in the wake reception and decode path 1004 and the barkerdetect and TIM decode path 1006. The decode functions of barker detectand TIM decode path 1006 are performed by separate, low power circuitryand the decode functions of wake reception and decode path along withthe functions of controller 1010 are performed by a processing core onthe integrated circuit under the control of software to perform thesteps of method 600 (FIG. 6).

In an example aspect, an integrated circuit includes an input coupled toreceive a plurality of beacon frames, the beacon frames include anindication of data transmissions available for a device that includesthe integrated circuit. The integrated circuit also includes acontroller configured to compare the plurality of beacon frames todetermine a plurality of bytes prior to the indication of datatransmission available that is present in each of the plurality ofbeacon frames and is configured to provide a signal indicating a lowpower mode in which the device does not receive transmissions and toprovide a signal indicating a wake mode at a selected time beforetransmission of the plurality of bytes in a subsequent beacontransmission.

In another example aspect, the beacon frames are received from an accesspoint.

In an example aspect, the indication of data transmissions available isa Traffic Indication Map (TIM).

In an example aspect, the plurality of bytes is at least twelve bytes.

In another example aspect, the plurality of bytes is at least apredetermined time prior to the indication of data transmissions.

In another example aspect, the input includes a first data path fordecoding the beacon frames and a second data path, the second data pathis configured to watch the beacon frames for the plurality of bytes, thecontroller provides a signal selecting one of the first and second datapaths.

In an example aspect, the beacon frame is part of a Wi-Fi transmission.

In another example aspect, a wireless station includes an antennaconfigured to receive a plurality of beacon frames, the beacon framesincluding an indication of data transmissions available for the wirelessstation. The wireless station also includes a controller configured tocompare the plurality of beacon frames to determine a plurality of bytesprior to the indication of data transmission available that is presentin each of the plurality of beacon frames and is configured to provide asignal indicating a low power mode in which the device does not receivetransmissions and to provide a signal indicating a wake mode at aselected time before transmission of the plurality of bytes in asubsequent beacon transmission.

In another example aspect, the beacon frames are transmitted from anaccess point.

In an example aspect, the indication of data transmissions available isa Traffic Indication Map (TIM).

In another example aspect, the plurality of bytes is at least twelvebytes.

In yet another example aspect, the plurality of bytes is at least apredetermined time prior to the indication of data transmissions.

In another example aspect, the antenna includes a first data path fordecoding the beacon frames and a second data path, the second data pathconfigured to watch the beacon frames for the plurality of bytes, thecontroller providing a signal selecting one of the first and second datapaths.

In an example aspect, a method of operation includes receiving aplurality of beacon frames, the beacon frames including an indication ofdata transmissions available for a device. The plurality of beaconframes is compared to determine a plurality of bytes prior to theindication of data transmission available that is present in each of theplurality of beacon frames. A signal is provided indicating a low powermode in which transmissions are not received. A signal indicating a wakemode is provided at a selected time before transmission of the pluralityof bytes in a next beacon transmission.

In another example aspect, the beacon frames are transmitted from anaccess point.

In another example aspect, the indication of data transmissionsavailable is a Traffic Indication Map (TIM).

In another example aspect, the plurality of bytes is at least twelvebytes.

In yet another example aspect, the plurality of bytes is at least apredetermined time prior to the indication of data transmissions.

In another example aspect, the method includes receiving transmissionsusing a first data path for decoding the beacon transmission during thewake mode. Transmissions are also received using a second data pathduring the low power mode, the second data path configured to watch forthe plurality of bytes.

In another example aspect, the beacon frame is part of a Wi-Fitransmission.

Modifications are possible in the described example aspects, and otheralternative arrangements are possible, within the scope of the claims.

What is claimed is:
 1. An integrated circuit comprising: an inputconfigured to communicatively receive: a first beacon frame, the firstbeacon frame including a first indication of a first data transmission;a second beacon frame, the second beacon frame including a secondindication of a second data transmission; and a third beacon frameincluding an indicator of available data transmissions; and a controllercoupled to the input and configured to: compare the first and secondbeacon frames to determine a plurality of bytes that is present in thefirst and second beacon frames; determine whether the received thirdbeacon frame includes the determined plurality of bytes; if the receivedthird beacon frame does not include the determined plurality of bytes,provide a signal indicating a low power mode; and if the received thirdbeacon frame includes the determined plurality of bytes, provide asignal indicating a wake mode before transmission of the plurality ofbytes in a subsequent beacon frame transmission.
 2. The integratedcircuit of claim 1 in which the beacon frames are received from anaccess point.
 3. The integrated circuit of claim 1 in which theindicator of available data transmissions is a Traffic Indication Map(TIM).
 4. The integrated circuit of claim 1 in which the plurality ofbytes is at least twelve bytes.
 5. The integrated circuit of claim 1 inwhich the plurality of bytes is received at least a predetermined timeprior to the third beacon frame.
 6. The integrated circuit of claim 1 inwhich the input includes a first data path during the wake mode and asecond data path, the second data path configured to receive asubsequent beacon frame, the controller providing a signal selecting oneof the first and second data paths.
 7. The integrated circuit of claim 1in which the beacon frame is part of a Wi-Fi transmission.
 8. A wirelessstation comprising: an antenna configured to communicatively receive: afirst beacon frame, the first beacon frame including a first indicationof a first data transmissions; a second beacon frame, the second beaconframe including a second indication of a second data transmission; and athird beacon frame including an indicator of available datatransmissions; a controller coupled to the antenna and configured to:compare the first and second beacon frames to determine a plurality ofbytes that is present in the first and second beacon frames; determinewhether the received third beacon frame includes the determinedplurality of bytes; if the received third beacon frame does not includethe determined plurality of bytes, provide a signal indicating a lowpower mode, and if the received third beacon frame includes thedetermined plurality of bytes, provide a signal indicating a wake modeat a selected time before transmission of the plurality of bytes in asubsequent beacon transmission.
 9. The wireless station of claim 8 inwhich the beacon frames are received from an access point.
 10. Thewireless station of claim 8 in which the indicator of available datatransmissions is a Traffic Indication Map (TIM).
 11. The wirelessstation of claim 8 in which the plurality of bytes is at least twelvebytes.
 12. The wireless station of claim 8 in which the plurality ofbytes is received at least a predetermined time prior to the thirdbeacon frame.
 13. The wireless station of claim 8 in which the antennaincludes a first data path and a second data path, the second data pathconfigured to receive a subsequent beacon frame, and the controller isconfigured to provide a signal selecting one of the first and seconddata paths.
 14. A method of operation comprising: receiving a firstbeacon frame, the first beacon frame including a first indication ofavailable data transmissions; receiving a second beacon frame, thesecond beacon frame including a second indication of a second datatransmission; comparing the first and second beacon frames to determinea plurality of bytes that is present in the first and second beaconframes; and receiving a third beacon frame, the third beacon frameincluding an indicator of available data transmissions; determiningwhether the received third beacon frame includes the determinedplurality of bytes; if the received third beacon frame does not includethe determined plurality of bytes, providing a signal indicating a lowpower mode; and the received third beacon frame includes the determinedplurality of bytes providing a signal indicating a wake mode beforetransmission of the plurality of bytes in a subsequent beacontransmission.
 15. The method of claim 14 in which the beacon frames arereceived from an access point.
 16. The method of claim 14 in which theindicator of available data transmissions is a Traffic Indication Map(TIM).
 17. The method of claim 14 in which the plurality of bytes is atleast twelve bytes.
 18. The method of claim 14 in which the plurality ofbytes is received at least a predetermined time prior to the thirdbeacon frame.
 19. The method of claim 14 further comprising: receivingtransmissions using a first data path during the wake mode; andreceiving transmissions using a second data path during the low powermode, the second data path configured to receive the subsequent beacontransmission.
 20. The method of claim 14 in which the first beacon frameis part of a Wi-Fi transmission.